1. Field of the Invention
The present invention relates to screw measuring methods, screw measuring probes, and screw measuring apparatuses using the screw measuring probes, and more particularly, to an improvement of an automatic method (mechanism) for measuring the effective diameter of a female screw.
2. Prior Art
Screws have been conventionally used to clamp various components. Since screws largely affect the quality and life time of the entire product in which the screws are used, it is very important to inspect them to maintain the quality thereof in a manufacturing process for machining them precisely. In screw inspection, characteristic values of the shape of each screw are measured, such as the effective depth, the pitch, the effective diameter, the thread angle, and the threading length.
For example, the three-wire method is often used to measure the effective diameter of a male screw. In the three-wire method, a three-wire gauge is applied to the groove of the male screw, the external dimension is measured with a micrometer, and the effective diameter of the male screw is obtained from the measured external dimension.
Since the three-wire method is a manual measurement method, skill in handling a three-wire gauge is required. Because micrometer readings may differ from operator to operator, it is difficult to maintain measurement precision and the efficiency of the measurement work.
Therefore, simplified measurement has been demanded in the field of screw measurement. To satisfy such a demand, a measurement method of measuring the dimensions of various shape characteristics of screws by the use of a three-dimensional measurement machine has been proposed (such as that disclosed in Japanese Unexamined Patent Application Publication No. 2001-82952).
In the method described in Japanese Unexamined Patent Application Publication No. 2001-82952, a three-dimensional measurement machine subjects a screw to profiling measurement using a probe and applies data processing to the results of the profiling measurement to obtain the dimensions of various shape characteristics of the screw. To obtain the effective diameter of a female screw, a virtual circle is applied to the shape data obtained from the profiling measurement and then, the three-wire method is used.
Even with the method described in Japanese Unexamined Patent Application Publication No. 2001-82952, the accuracy of an effective diameter obtained in automatic measurement needs to be further improved, and in particular, it is difficult to measure the effective diameter of a female screw automatically.
Conventionally, there is no suitable conventional technology to solve this issue. Although a three-dimensional measurement machine has been used to measure the effective diameter of a female screw, an appropriate machine for automatic measurement of the effective diameter of a female screw has not been developed.